diff --git a/api/openapi.yaml b/api/openapi.yaml
index b20f677..6439c86 100644
--- a/api/openapi.yaml
+++ b/api/openapi.yaml
@@ -196,7 +196,7 @@ paths:
     #               error:
     #                 type: string
 
-  # /users:
+  /users:
   #   get:
   #     summary: Search user
   #     parameters:
@@ -218,28 +218,28 @@ paths:
   #               items:
   #                 $ref: '#/components/schemas/User'
 
-  #   post:
-  #     summary: Add new user
-  #     requestBody:
-  #       required: true
-  #       content:
-  #         application/json:
-  #           schema:
-  #             $ref: '#/components/schemas/User'
-  #     responses:
-  #       '200':
-  #         description: Add result
-  #         content:
-  #           application/json:
-  #             schema:
-  #               type: object
-  #               properties:
-  #                 success:
-  #                   type: boolean
-  #                 error:
-  #                   type: string
-  #                 user_json:
-  #                   $ref: '#/components/schemas/User'
+    post:
+      summary: Add new user
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/User'
+      responses:
+        '200':
+          description: Add result
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  success:
+                    type: boolean
+                  error:
+                    type: string
+                  user_json:
+                    $ref: '#/components/schemas/User'
 
 #   /users/{user_id}/titles:
 #     get:
@@ -580,7 +580,7 @@ components:
       required:
         - user_id
         - nickname
-        - creation_date
+        # - creation_date
     UserTitle:
       type: object
       additionalProperties: true
diff --git a/sql/migrations/000001_init.up.sql b/sql/migrations/000001_init.up.sql
index 0b7fa33..abecd32 100644
--- a/sql/migrations/000001_init.up.sql
+++ b/sql/migrations/000001_init.up.sql
@@ -27,8 +27,8 @@ CREATE TABLE users (
     id                  bigint              GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
     avatar_id           bigint              REFERENCES images (id),
     passhash            text                NOT NULL,
-    mail                text                CHECK (mail ~ '[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9_-]+'),
-    nickname            text                NOT NULL CHECK (nickname ~ '^[a-zA-Z0-9_-]+$'),
+    mail                text                CHECK (mail ~ '^[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9_-]+$'),
+    nickname            text                UNIQUE NOT NULL CHECK (nickname ~ '^[a-zA-Z0-9_-]{3,}$'),
     disp_name           text,
     user_desc           text,
     creation_date       timestamptz         NOT NULL,
@@ -85,6 +85,12 @@ CREATE TABLE signals (
     pending             boolean             NOT NULL
 );
 
+CREATE TABLE external_ids (
+    user_id                                 NOT NULL REFERENCES users (id),
+    service_id          text                NOT NULL,
+    external_ids        text                NOT NULL
+);
+
 -- Functions
 CREATE OR REPLACE FUNCTION update_title_rating()
 RETURNS TRIGGER AS $$